The present invention relates to a liquid crystalline polyester, particularly a liquid crystalline polyester which permits its orientation in the state of liquid crystal to be immobilized easily as glass phase and which is suitable for application to optical elements.
Recently, as to liquid crystalline polymers, researches and developments have been made actively in the field of high-performance materials utilizing high heat resistance and moldability and also in the field of functional materials utilizing phase immobilization and changes in the liquid crystal structure caused by heat or by an external field such as an electric field. In the high-performance material field, liquid crystalline polymers have already been commercialized. On the other hand, in the functional material field, researches have been made actively for attaining the application of such polymers to optical recording, non-linear optical materials, alignment film for liquid crystal, optical fiber and optical element for a liquid crystal display, but commercialization has not been made yet. In the case of using a liquid crystalline polymer as a functional material, a phase structure thereof obtained in the state of liquid crystal is immobilized for use in most cases.
It is a great attractive point of the liquid crystalline polymer that such immobilization can be made. But for making the immobilization possible and for the immobilized liquid crystal structure to be stable at a working temperature, it is absolutely necessary that the liquid crystalline polymer used should have a glass phase at a temperature lower than the liquid crystal transition point thereof. If there is used a polymer having a crystal phase at a temperature lower than the liquid crystal transition point thereof, it will be impossible to effect immobilization, or a liquid crystal structure thereof once immobilized will be relaxed with the lapse of time. Liquid crystalline polymers can be broadly classified into main chain type liquid crystalline polymers and side chain type liquid crystalline polymers. From the industrial standpoint, main chain type liquid crystalline polymers are preferred because they are less expensive and easier to manufacture. Particularly, liquid crystalline polyesters are preferred.
However, many polyesters are generally high in crystallinity and difficult to be immobilized, so their application to functional materials has not so progressed yet.
It is the object of the present invention to provide a novel liquid crystalline polyester which has a glass phase at a temperature lower than the liquid crystal transition point thereof and which permits an oriented structure thereof in the state of liquid crystal to be immobilized easily and is therefore suitable for application to various functional materials.